I would imagine that it is because of the original Greek, which states that,
á½‰ Î´á½² Î£Î±á¿¦Î»Î¿Ï‚, á¼”Ï„Î¹ á¼Î½Ï€Î½á½³Ï‰Î½ á¼€Ï€ÎµÎ¹Î»á¿†Ï‚ ÎºÎ±á½¶ Ï†á½¹Î½Î¿Ï… Îµá¼°Ï‚ Ï„Î¿á½ºÏ‚ Î¼Î±Î¸Î·Ï„á½°Ï‚ Ï„Î¿á¿¦ ÎºÏ…Ïá½·Î¿Ï…... (ÎºÏ„Î».)
Here, the present participle á¼Î½Ï€Î½á½³Ï‰Î½, "breathing," which is translated by the Latin spirans takes the genitive with the sense of "breathing of" or "being laden with," with á¼€Ï€ÎµÎ¹Î»á¿†Ï‚ "threat" and Ï†á½¹Î½Î¿Ï… "murder" corresponding to minarum and caedis.
Usage of á¼Î½Ï€Î½á½³Ï‰ + gen is also attested in Stobaeus, a 5th cent. Greek author, in his excerpts of the philospher Perictione.